I think adding fighters to any ship smaller than carriers is a bad idea. They’re hard enough to balance as it is on capital platforms. That kind of on-grid power projection should not come lightly.
Cost shouldn’t be the factor in balance, unless you’re talking mineral cost of T1 platforms. The issue is the huge gap in EHP and DPS, not the gap (or lack thereof) in price.
I’m still on the fence as to whether capitals should ever be allowed in hisec. At most, I think dreads and carriers could get away with limited access to the lower end of hisec (i.e. 0.7 and below) and some additional elements of risk (perpetual suspect, docking timers, etc.). But, like with the intermediate ship between battleships and dreads, there’s no real need for it. The closest things to proper justifications for such a move I’ve heard (full disclaimer, one of them is my own) are centered on lore which is kind of a sketchy way to handle game balance.
Hard no to Titans, Supers, and Rorqs in hisec anywhere though, and probably no FAXes either. Also hard no to “buying” access directly through ISK or PLEX as that would grossly favor large blocs over individuals or smaller groups.